Molten glass delivery apparatus for optical quality glass

ABSTRACT

A molten glass delivery system is modified to match it with the overflow downdraw process. A substantial number of defects not removed by the finer are diverted to the unusable inlet and distal edges of the sheet. In one embodiment, the stirring device is relocated from the outlet to the inlet of the finer. In another embodiment, the basic shape of the finer is preferably changed from a cylindrical shape to a Double Apex (or Gull Wing) shaped cross-section, whereby the apexes of the finer contain the glass that will form the unusable inlet end of the glass sheet. The finer vent or vents are preferably located at these apexes such that any homogeneity defects caused by the vents are diverted to the unusable inlet end of the glass sheet. The finer cross-section has a high aspect ratio for increased fining efficiency as compared to a cylindrical finer.

REFERENCE TO RELATED APPLICATIONS

This application claims one or more inventions which were disclosed inProvisional Application No. 60/954,622, filed Aug. 8, 2007, entitled“MOLTEN GLASS DELIVERY APPARATUS FOR THE OVERFLOW DOWNDRAW SHEET FORMINGPROCESS” and Provisional Application No. 60/957,007, filed Aug. 21,2007, entitled “MOLTEN GLASS DELIVERY APPARATUS FOR THE OVERFLOWDOWNDRAW SHEET FORMING PROCESS”. The benefit under 35 USC §119(e) of theUnited States provisional applications is hereby claimed, and theaforementioned applications are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the manufacture of optical qualityglass. More specifically, it is especially useful for the manufacture ofglass sheet made by the overflow downdraw process for the production ofTFT/LCD display devices that are widely used for television and computerdisplays.

2. Description of Related Art

The typical glass manufacturing process includes, in series, a rawmaterial storing, mixing, and feeding system, a glass melting furnace, amolten glass delivery system, a glass forming process, and a finishedglass handing system for cutting, cleaning, packaging and shipping.

FIG. 1 shows a typical “Overflow Process” manufacturing system (1). Themelting furnace (2) feeds liquid glass (16) of substantially uniformtemperature and chemical composition to the finer (3), which removes anygaseous inclusions through the finer vent (15) and feeds a stirringdevice (4), also known as a stirring apparatus (4). The stirring device(4), including one or more stirrers, thoroughly homogenizes the glass.The stirring device (4) is always placed after the finer (3) in theprior art, to remove inhomogeneities in the glass which may be createdin the finer (3).

The glass (16) is then conducted through a cooling and conditioningsection (5), into a bowl (6), and down into the downcomer pipe (7),through the joint (14) between the downcomer pipe (7) and the formingapparatus inlet pipe (8), to the inlet of the overflow trough (9). Whileflowing from the stirring device (4) to the trough (9), the glass (16),especially that which forms the sheet surface, must remain homogeneous.The bowl (6) alters the flow direction from horizontal to vertical andprovides a means for stopping the flow of glass (16). A needle (13) isoften provided to stop glass flow. The downcomer pipe (7) has twoprimary functions. It conducts the glass from the bowl (6) to the troughinlet pipe (8) and controls the flow rate of the glass (16) entering thesheet forming apparatus. The downcomer pipe (7) is carefully designedsuch that, by maintaining it at a specific temperature, the desiredglass (16) flow rate is precisely maintained at the desired value. Thefiner (3), the finer vent (15), the stirring device (4), the cooling andconditioning section (5), the bowl (6), the needle (13), and thedowncomer pipe (7) comprise the glass delivery system (10), whichconducts and conditions the glass (16) from the furnace to the top ofthe inlet pipe (8) of the overflow process. The joint (14) between thedowncomer pipe (7) and the trough inlet pipe (8) allows for removal ofthe sheet glass forming apparatus for service as well as providingcompensation for the thermal expansion of the process equipment.

The glass (16) flowing from the furnace (2) is at a high temperature(1500° to 1600° C.) and is a Newtonian liquid, but has gaseous inclusiondefects and is not a homogeneous mixture. The delivery system (10)delivers the glass to the overflow forming process at the correcttemperature (approximately 1225° C.), in a homogeneous state with aminimum of gaseous inclusions or other homogeneity defects.

The molten glass (16) from the delivery system (10), which must be ofsubstantially uniform temperature and chemical composition, enters thesheet forming apparatus through the inlet pipe (8) to the sheet formingtrough (9). The glass sheet forming apparatus, which is described indetail in U.S. Pat. Nos. 3,338,696, 6,748,765, and 6,889,526, hereinincorporated by reference, is a wedge shaped forming device (9). Theglass (16) then flows down each side of the wedge shaped forming device(9), and joins at the pointed bottom edge to form a sheet of moltenglass (11). The sheet of molten glass (11) is then cooled to form asolid glass sheet (12) of substantially uniform thickness.

Glass as melted from raw materials has many small bubbles of entrappedgases. These bubbles are considered defects in any glass product whichrequires optical properties. Bubbles of a size that can be seen by theeye or that interfere with the function of the product must be removed.The process for removing these bubbles is termed either fining ordegassing (fining herein). Fining occurs after the glass is melted fromraw materials, but before the glass is formed into a finished product.In optical quality glass, this fining process is performed in a “finer”(or refiner), which is constructed of precious metal, typically platinumor a platinum alloy. The fining process is both chemical and physical.Chemicals, termed fining agents, are added to the glass such that thebubbles grow in size as they pass through the glass melting furnace andthe finer. Arsenic or Antimony as oxides in the glass are preferredfining agents, but are toxic materials. Tin is another commonly usedfining agent, but it is less effective as a fining agent and itchemically reduces platinum, producing tiny particles and causingeventual destruction of the platinum walls. Cerium may also be used as afining agent, but colors the glass yellow. These are the most used amongthe fining agents, however, there are others known in the art.

Optical quality glass is unique in that disruptions in the flow pathoften produce a homogeneity defect. This defect class is called cord andit produces optical distortion in the product. The finer often isdesigned with baffles as discussed herein. Baffles and the finer vent(15) or vents produce significant flow disruptions. For this reason, inthe prior art, the stirring device (4) is placed after the finer (3) inthe flow path such that inhomogeneities from the finer are homogenized.Both the finer and stirring device operate at a high temperature ofapproximately 1600° C. The glass discharged from the stirring device issubstantially homogeneous, although the stirring device (4) can itselfproduce a homogeneity defect, which is discussed herein. To minimize thefurther creation of inhomogeneities, the cooling and conditioning pipe(5), the bowl (6), and the downcomer pipe (7) are carefully finished(smoothed) on the glass contact surfaces to minimize flow pathdisruptions. In the delivery system, it is desirable to maintain theflow uniform with no regions of quiescent or recirculating flow and aminimum exposure to the atmosphere. Exposure to the atmosphere can causevolatilization of some of the glass chemicals and thus change the glasscomposition and properties, potentially introducing homogeneity defects.The temperature of the glass in the delivery system must be maintainedabove the liquidus temperature of the glass to prevent recrystallization(devitrification) of the glass, which would be an optical defect. Thebowl, which in many designs has a free surface, can be a source of cordand devitrification defects.

The fining apparatus is designed such that the removal of the bubblesfrom the molten glass is optimized. The finer is often very large,resulting in extremely high costs to fabricate because the glass contactsurfaces are constructed of platinum or platinum alloy. In the prior artfining process, the bubbles rise to the top of the fining apparatus(finer) where they dissipate to the atmosphere through the finer vent(15). The size of the bubbles that are removed is a function of the sizeand design of the finer and the viscosity (fluidity) of the moltenglass. In the glass industry, these bubbles are called seeds if they aresmall (less than approximately 1 mm diameter) and blisters if they arelarge. Seeds are the primary concern as they are small in diameter andtherefore are more difficult to remove from the glass.

The glass seed entering the finer at the bottom of the inflow end of thefiner must rise to the top of the finer at the outflow end where a ventto the atmosphere is located. The vertical speed of a seed in glass isinversely proportional to the glass viscosity, proportional to thesquare of the seed diameter, and proportional to the square of the glassdensity. The glass viscosity is a strong inverse function oftemperature, therefore raising the glass temperature to a practicalmaximum increases the vertical speed of a given size seed. The detectionof a seed in an optical product is a strong function of its viewablearea, therefore one can use the diameter squared of a seed as thequality criteria. For a given glass, the variation of the glass densityin the fining process is a second order effect.

At the very high temperatures, approximately 1600° C., required tosubstantially reduce the glass viscosity, even the highest qualityrefractory materials are slowly dissolved by the glass. This introducescontamination and can also generate additional seeds in the glass. Inthe prior art, a cylindrical platinum or platinum alloy (platinumherein) tube is used for all surfaces (walls) that contact the glass,such that the glass is not contaminated by the dissolution of refractorywalls. The cylindrical tube is typically supported externally byrefractory material (brick), which has the appropriate strength andinsulating properties. The glass in the finer must be maintained at therequired elevated temperature. Additionally, the glass entering theinflow end of the finer often must be heated to the desired finingtemperature. This is done by either containment of the platinum andrefractory finer assembly in a heated (gas or electric) firebox or byelectrical heating. The electrical heating of the finer is accomplishedby either externally mounted electric windings (normally made ofplatinum) or the passing of electric current directly through thecylindrical platinum tube, thus using the electrical resistance of thetube to generate the heat.

The prior art design which has been typically used since the start ofthis practice in the first half of the twentieth century is acylindrical platinum tube either with or without internal baffles. Theprimary innovations to date have been in the design of the baffles toalter the flow path and to trap seeds for optimal seed removal. Theprior art includes finer designs with and without an internal freesurface.

FIG. 2A is a typical baffled finer of the prior art. The molten glass(16) enters the baffled finer (21) at the glass inlet end (23) and flowsout the outlet (24). There is a vent (25) at the outlet end (24), whichis connected to the atmosphere, to allow the seeds which accumulate atthe top of the baffled finer (21) to escape. Some of the baffles (26)have holes (22), which are sized to distribute the flow of the moltenglass (16) such that the average residence time for the glass as itflows through the baffled finer (21) is more uniform. Other baffles (28)are designed to move the flow path vertically. There is often a vent(29) in front of a baffle, as baffles also trap the surface seeds into afoam-like accumulation, which breaks down and dissipates into theatmosphere. FIG. 2B shows the movement of seeds (27) through the baffledfiner (21). The baffles (26) and (28) make the paths of the seeds (27)in the baffled finer (21) quite tortuous. This allows the smaller seedsgreater opportunity to coalesce together and form a larger seed, whichin turn will rise faster.

The finer shown in FIGS. 2A and 2B has a diameter of 0.382 meters and alength of 2.5 meters. The glass flow rate is 7.41 metric tons per day.The glass viscosity is 100 poise. The seed diameter is 0.0007 meters.These parameters can be changed by normalizing using the equation:

Q ₁ *d ₁ ²/η₁ =Q ₀ *d ₀ ²/η₀

where:

Q equals glass flow,

η equals glass viscosity, and

d equals seed diameter

The prior art stirring device (4) consists of one or more rotatingelements. The glass at the tip of the final rotating element is oftentrapped in a vortex. Glass exiting this vortex has a rotating motion anda different time history than the glass in the main flow path. This canresult in a cord homogeneity defect if this glass is part of the salableportion of the product.

DRAWBACKS OF THE PRIOR ART

A major drawback of the prior art is that the homogenization of theglass after the fining operation redistributes any defects not removedby the finer throughout the entire glass stream.

Another drawback specific to tin refined glasses is that the platinumparticles, which are caused by the chemical reduction of platinum by tinin the finer and which would normally flow close to the delivery systemsurfaces, are redistributed throughout the entire sheet by the stirringof the glass after it has been processed by the finer.

Another drawback is that the inhomogeneous glass discharged from the tipof the stirrer creates defects in the formed glass sheet. Yet anotherdrawback is the inhomogeneous glass discharged from the free surface inthe bowl.

Another drawback is that the use of temperature to control glass flowrate has an inherent low control bandwidth.

Another drawback is that the solid connection of the melting furnace tothe delivery system prevents major repair or rebuild of the meltingfurnace without also rebuilding a major portion of the delivery system.

SUMMARY OF THE INVENTION

The present invention significantly modifies the prior art glassdelivery system from the furnace to the glass forming process to matchit with the overflow downdraw process. A substantial number of defectsnot removed by the finer are diverted to the unusable inlet and distaledges of the sheet. In one embodiment, the stirring device is relocatedto the inlet of the finer from the outlet of the finer. In anotherembodiment, the basic shape of the finer is preferably changed from acylindrical shape to a Double Apex (or Gull Wing) shaped cross-sectionwhereby the apexes of the finer contain the glass that will form theunusable inlet end of the glass sheet. The finer vent or vents arepreferably located at these apexes such that any homogeneity defectscaused by the vents are diverted to the unusable inlet end of the glasssheet. The finer cross-section has a high aspect ratio for increasedfining efficiency as compared to a cylindrical finer.

Another embodiment eliminates the bowl and the needle. In otherembodiments, the finer vent may be eliminated when the apparatus isbeing used with some specific glasses. In additional embodiments, glasslevel measuring devices are preferably installed at the finer vents. Inyet another embodiment, baffles are added to the bottom of the downcomerpipe to divert flow that is adjacent to the downcomer pipe surface intothe unusable inlet and distal edges of the sheet.

In another embodiment the stirrer speed is used to increase thebandwidth of glass flow rate control.

In another embodiment, the fixed connection of the delivery system tothe melting furnace is replaced with an adjustable and flexibleconnection so that a melting furnace that is no longer functioning canbe easily removed from the delivery system for repair or replacement.

The present invention improves the fining capability of the deliverysystem apparatus by matching the flow characteristic of the deliverysystem to the overflow downdraw process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the principle parts of “The Overflow Process” glasssheet manufacturing system.

FIG. 2A shows a cylindrical finer with baffles as known in the priorart.

FIG. 2B shows the rising of seeds in the finer of FIG. 2A.

FIG. 3 shows the principle parts of “The Overflow Process” glass sheetmanufacturing system in an embodiment of the present invention.

FIG. 4A shows a side view of “The Overflow Process” as known in theprior art.

FIG. 4B shows a cross-section of the glass flow in the downcomer pipeacross lines B-B of FIG. 4A.

FIG. 4C shows a cross-section across lines C-C of FIG. 4A, where theglass flow in the downcomer pipe appears in the sheet for “The OverflowProcess”.

FIG. 5 shows a cross-section of a Double Apex finer at the location ofatmospheric vents and the location of the glass that flows to the inletand distal edges of the sheet.

FIG. 6 shows the principle parts of “The Overflow Process” glass sheetmanufacturing system in an embodiment of the present invention.

FIG. 7A shows the principle parts of “The Overflow Process” glass sheetmanufacturing system in an embodiment of the present invention.

FIG. 7B shows a cross-section of a stirring device that will alter glassflow rate in an embodiment of the present invention.

FIG. 7C shows a cross-section of the stirring device across lines C-C ofFIG. 7B.

FIG. 8A shows flow diverters located at the bottom of the downcomer pipein an embodiment of the present invention.

FIG. 8B shows a cross-section of the downcomer pipe in an embodiment ofthe present invention, across lines B-B of FIG. 8A.

FIG. 8C shows a cross section of the downcomer pipe in an embodiment ofthe present invention, across lines C-C of FIG. 8B.

FIG. 9A shows a high aspect ratio dual apex finer cross-section withgenerous corner radii in an embodiment of the present invention.

FIG. 9B shows a high aspect ratio dual apex finer cross-section withsharp corners in an embodiment of the present invention.

FIG. 9C shows a high aspect ratio dual apex finer cross-section withchamfered corners in an embodiment of the present invention.

FIG. 9D shows a high aspect ratio dual apex finer cross-section withmodest corner radii and an extended vent cross-section with an internalfree surface in an embodiment of the present invention.

FIG. 10A shows a high aspect ratio dual apex finer cross-section withgenerous corner radii and a flat bottom in an embodiment of the presentinvention.

FIG. 10B shows a low aspect ratio dual apex finer cross-section withgenerous corner radii and a V shaped bottom in an embodiment of thepresent invention.

FIG. 10C shows a cylindrical finer cross-section modified to a dual apexconfiguration in an embodiment of the present invention.

FIG. 10D shows an elliptical finer cross-section modified to a dual apexconfiguration in an embodiment of the present invention.

FIG. 11A shows the principle parts of “The Overflow Process” glass sheetmanufacturing system with a sloped finer in an embodiment of the presentinvention.

FIG. 11B shows a cross-section of a finer vent containing a mechanicalglass level measuring device in an embodiment of the present invention.

FIG. 12A shows the principle parts of “The Overflow Process” glass sheetmanufacturing system with a sloped finer in an embodiment of the presentinvention.

FIG. 12B shows a cross-section of a finer vent containing a laser glasslevel measuring device in an embodiment of the present invention.

FIG. 13 shows the principle parts of “The Overflow Process” glass sheetmanufacturing system whereby the stirring device has pumping action thatflows glass from the melting furnace to the forming process in anembodiment of the present invention.

FIG. 14A shows a high aspect ratio free surface finer cross-section withgenerous corner radii and a shallow V shaped bottom in an embodiment ofthe present invention.

FIG. 14B shows a low aspect ratio free surface finer cross-section withgenerous corner radii and a V shaped bottom in an embodiment of thepresent invention.

FIG. 14C shows a cylindrical free surface finer cross-section modifiedto a flat top configuration in an embodiment of the present invention.

FIG. 14D shows an elliptical free surface finer cross-section modifiedto a flat top configuration in an embodiment of the present invention.

FIG. 15A shows the principle parts of “The Overflow Process” glass sheetmanufacturing system with a sloped finer with a full length free surfaceand an overflow device at the downcomer to inlet pipe interface in anembodiment of the present invention.

FIG. 15B shows a cross-section of a full length free surface finer shownin FIG. 15A containing a surface baffle at the finer vent in anembodiment of the present invention.

FIG. 16A shows the location of the overflow device at the downcomer toinlet pipe interface in an embodiment of the present invention.

FIG. 16B is a top view of the overflow device in an embodiment of thepresent invention.

FIG. 16C is a side view section showing the bottom of the overflow pipelocated below the glass free surface in the overflow device in anembodiment of the present invention.

FIG. 16D is a side view section showing the bottom of the overflow pipelocated above the glass free surface in the overflow device in anembodiment of the present invention.

FIG. 17A is a side view of the application of the dual apex principle toa bowl in an embodiment of the present invention.

FIG. 17B is an end view of the application of the dual apex principle toa bowl in an embodiment of the present invention.

FIG. 18 shows the principle parts of “The Overflow Process” glass sheetmanufacturing system with an overflow device in the bowl in anembodiment of the present invention.

FIG. 19 shows the principle parts of “The Overflow Process” glass sheetmanufacturing system with a sloped finer with a full length free surfaceand an overflow device in the bowl in an embodiment of the presentinvention.

FIG. 20A shows one use of radii in a high aspect ratio enclosed finer.

FIG. 20B shows another use of radii in a high aspect ratio enclosedfiner.

FIG. 20C shows another use of radii in a high aspect ratio enclosedfiner.

FIG. 21A shows one use of chamfers in a high aspect ratio enclosedfiner.

FIG. 21B shows another use of chamfers in a high aspect ratio enclosedfiner.

FIG. 21C shows another use of chamfers in a high aspect ratio enclosedfiner.

FIG. 22A shows one use of radii in a high aspect ratio free surfacefiner.

FIG. 22B shows another use of radii in a high aspect ratio free surfacefiner.

FIG. 22C shows another use of radii in a high aspect ratio free surfacefiner.

FIG. 23A shows one use of chamfers in a high aspect ratio free surfacefiner.

FIG. 23B shows another use of chamfers in a high aspect ratio freesurface finer.

FIG. 23C shows another use of chamfers in a high aspect ratio freesurface finer.

FIG. 24A shows a six sided finer cross-section with an inverted apexgable roof and radii at the ends in an embodiment of the presentinvention.

FIG. 24B shows a six sided finer cross-section with an inverted apexgable roof, fining ribs and chamfered ends in an embodiment of thepresent invention.

FIG. 24C shows a six sided finer cross-section with an inverted apexGothic arch roof and radii at the ends in an embodiment of the presentinvention.

FIG. 24D shows a six sided finer cross-section with an inverted apexGothic arch roof, fining ribs and corner vents at the ends in anembodiment of the present invention.

FIG. 25 shows an inverted apex gable roof finer with fully radiusedends.

FIG. 26 shows a finer with multiple cross sections in an embodiment ofthe present invention.

FIG. 27A shows a cylindrical cross-section of a finer as known in theprior art.

FIG. 27B shows an elliptical cross-section of a finer in an embodimentof the present invention.

FIG. 27C shows a square cross-section of a finer.

FIG. 27D shows a rectangular cross-section of a finer in an embodimentof the present invention.

FIG. 27E shows a rectangular with chamfered sides cross-section of afiner in an embodiment of the present invention.

FIG. 27F shows a rectangular with curved sides cross-section of a finerin an embodiment of the present invention.

FIG. 27G shows a rectangular with curved sides and an arced top andbottom cross-section of a finer in an embodiment of the presentinvention.

FIG. 27H shows a cross-sectional shape similar to FIG. 4G, except thetop and bottom surfaces are not parallel.

FIG. 28A shows a five sided gable roof finer cross-section in anembodiment of the present invention.

FIG. 28B shows a six sided gable roof finer cross-section in anembodiment of the present invention.

FIG. 28C shows a six sided gable roof finer cross-section with finingribs in an embodiment of the present invention.

FIG. 28D shows a six sided gable roof finer cross-section with finingribs and chamfered ends in an embodiment of the present invention.

FIG. 28E shows a six sided gable roof finer cross-section with radii atthe ends in an embodiment of the present invention.

FIG. 28F shows a six sided gable roof finer cross-section with radii andchamfers at the ends in an embodiment of the present invention.

FIG. 28G shows a seven sided gable roof finer cross-section with radiiat the ends in an embodiment of the present invention.

FIG. 28H shows a six sided gable roof finer cross-section with finingribs and chamfered ends in an embodiment of the present invention.

FIG. 29A shows a five sided Gothic arch roof finer cross-section in anembodiment of the present invention.

FIG. 29B shows a six sided Gothic arch roof finer cross-section in anembodiment of the present invention.

FIG. 29C shows a seven sided Gothic arch roof finer cross-section withfining ribs in an embodiment of the present invention.

FIG. 29D shows a six sided Gothic arch roof finer cross-section withfining ribs and chamfered ends in an embodiment of the presentinvention.

FIG. 29E shows a five sided Gothic arch roof finer cross-section with acurved bottom and radii at the ends in an embodiment of the presentinvention.

FIG. 29F shows a six sided Gothic arch roof finer cross-section withradii and chamfers at the ends in an embodiment of the presentinvention.

FIG. 29G shows a seven sided Gothic arch roof finer cross-section withradii at the ends in an embodiment of the present invention.

FIG. 29H shows a six sided Gothic arch roof finer cross-section withfining ribs and chamfered ends in an embodiment of the presentinvention.

FIG. 30 shows the principle parts of “The Overflow Process” glass sheetmanufacturing system whereby the stirring device has pumping action thatflows glass from the melting furnace to the forming process in anembodiment of the present invention.

FIG. 31A shows a detail of an interface between a melting furnaceforebay and the stirring device in an embodiment of the presentinvention.

FIG. 31B shows a detail of an interface between a melting furnaceforebay and the stirring device in an embodiment of the presentinvention.

FIG. 32A shows one embodiment of a fluid connection between a meltingfurnace and a finer.

FIG. 32B shows another embodiment of a fluid connection between amelting furnace and a finer.

FIG. 33 shows another embodiment of a fluid connection between a meltingfurnace and a finer.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the apparatus termed the deliverysystem, which transfers and conditions the glass from the furnace to theforming process. The flow characteristics of the glass in the overflowdowndraw process are unique and of a character that has led to theinvention of a new configuration of the delivery system. The presentinvention reorganizes and redesigns the component parts of the deliverysystem and allows for the use of equipment thought detrimental to thequality requirements of the overflow downdraw process.

The present invention is related to the physical aspect of fining, whichis affected by the shape of the finer apparatus. Specifically, in oneembodiment, the shape of the fining apparatus in the present inventionis matched to the flow characteristics of the overflow downdraw sheetglass manufacturing process. For a given glass, the variation of theglass density in the fining process is a second order effect, thus thepresent invention considers primarily the glass viscosity and the seedcross-sectional area.

The finer configuration that is used in the embodiments of the presentinvention preferably has a high aspect ratio (high width to heightratio) to give increased fining performance as compared to thecylindrical finer used in the prior art. Examples of high aspect ratiofiners are shown in U.S. Pat. No. 7,150,165 and U.S. Patent Publication2007/0084247, which are incorporated herein by reference.

The present invention significantly modifies the prior art glassdelivery system (10) from the glass melting furnace to the sheet formingapparatus to match it with the overflow downdraw process. The presentinvention includes a glass delivery system which homogenizes the glass,removes most of the seeds and blisters from the glass, and thendistributes most of the remaining defects to the unusable inlet anddistal edges of the glass sheet which is formed by the overflow downdrawprocess. Two important elements of the present invention are relocatingthe stirring device to the inlet of the finer and designing the finer sothat defects caused by the finer end up in the unusable ends of thesheet. Unless otherwise indicated, in all of the embodiments, thestirring device is relocated to the inlet of the finer from the outletof the finer.

To achieve the maximum benefits of this invention, the simultaneous useof all of the embodiments as a system is preferred; however, any of theindividual embodiments may alternatively be used or implementedindependently of each other. The actual production implementation of theembodiments of this invention would likely be in rational steps aschange in a manufacturing environment is almost always cautious.

The description of the embodiments of this invention is made in an orderthat they might be implemented into the system and in an order that iseasily described. Other orders for implementing, as well as use of theindividual embodiments separately, are within the spirit of the presentinvention.

FIG. 3 represents an embodiment of a delivery system (30), where thestirring device (34) is relocated to the inlet of the finer from theoutlet of the finer. The basic shape of the finer (33) is changed from acylindrical shape to a shaped cross-section as shown in FIGS. 5, 9Athrough 9D, and 10A through 10D, whereby the apexes (57) of the finercontain the glass that will form the unusable inlet end of the glasssheet. The finer vents (35 and 55) are located at these apexes (57) suchthat any homogeneity defects caused by the vents are diverted to theunusable inlet end of the glass sheet.

FIGS. 4A through 4C illustrate where the glass (16) flowing in thedowncomer feed pipe (7) ends up in the formed glass sheet in the priorart “Overflow Process”. The glass flow (41) in proximity to the sidesurfaces of the downcomer pipe (7) as shown in FIG. 4B ends up formingthe center of the drawn sheet as shown in FIG. 4C. The flow (43) inproximity to the front surface of the downcomer pipe (7) as shown inFIG. 4B is distributed over the entire glass surface; however, it ismost concentrated on the approximately one third of the sheet at theinlet end as shown in FIG. 4C. This surface glass (43) is subject todisruption by the downcomer pipe surface and by the glass in thequiescent zones in the bowl (6) and at the downcomer pipe (7) to inletpipe (8) connection (14). The surface of the remaining substantially twothirds of the sheet is formed from virgin interior glass (42) as shownin FIG. 4B. Two other portions of the glass flow (44) which aresymmetrically offset from the front surface at an angle of approximately45 degrees as shown in FIG. 4B end up forming the near end unusable edgesection (45) at the inlet end of the sheet as shown in FIG. 4C. Anotherportion (46) centered at an angle of approximately 180 degrees proceedsas shown in FIG. 4B to the far end unusable edge section (47) as shownin FIG. 4C. The inlet end section (45) and the distal end section (47),as shown in FIG. 4C, includes the portions of the sheet which do notmeet the thickness and flatness specifications and thus are notsaleable. In this invention, the design of the delivery system,primarily the finer, is such that the homogeneity defects and a largeportion of the remaining seed defects are diverted to these endsections.

FIG. 5 shows the cross-section (50) of a Double Apex (or Gull Wingshaped) finer at the finer vents (55) in an embodiment of the presentinvention. The finer vents (55) may be vented directly to the factoryatmosphere or vented filter and/or vacuum system. This finer has a highwidth to height ratio to give increased fining performance as documentedin U.S. Pat. No. 7,150,165 and U.S. Patent Publication No. 2007/0084247.The finer vents (55) are located at the apexes (57) of the finercross-section. The dimensions of the finer and delivery system are suchthat the glass in the areas (54) that flows past these apexes (57) isthe glass that will flow to the area (44) as shown in FIG. 4C of theformed sheet (11). Any glass inhomogeneities that are caused by thefiner vents to the glass in the areas (54) thus end up in the area (44),the unusable inlet end of the glass sheet. Also, seeds which have risento the area (54), the proximity of the finer vents (55), but are nottrapped by the vents (55), will also flow to the area (44) in the formedsheet. The free surface (58) of glass in the finer is shown located inthe vent above the apex (57). The vertical position of the free surface(58) may vary over a distance (59) without affecting the intendedperformance of this invention.

FIG. 6 shows another embodiment of a delivery system (60) of the presentinvention where the bowl (6) in the prior art is replaced by atransition section (66). The transition section (66) insures smoothglass flow from the cooling and conditioning pipe (5) to the downcomerpipe (7) and thus there is no free surface in the transition section(66). There is a glass free surface in the finer vent (35), whichreplaces the free surface normally in the bowl (6). A glass free surfaceis important for the stabilization of flow in the downcomer pipe (7).

FIG. 7A shows another embodiment of a delivery system (70) of thepresent invention where the finer (73) exits from the bottom portion ofthe stirring device (34) with a formed section (77) and the finer (73)has no vent. This finer is designed for use with glasses that generatefew seeds during the melting process, such as the glass described inU.S. Patent Publication 2006/0293162, herein incorporated by reference.The seeds that are produced in the melting of the glass will rise to thearea (54) at the apexes (57) of the finer as shown in FIG. 5 and flow tothe area (44) of the formed sheet as shown in FIG. 4C.

FIG. 7B is a section through the center of the stirring device (34) andshows two stirrers (71 and 72). The molten glass (16) from the meltingfurnace (2) flows into the stirring device (34) at the entrance (78),vertically upward past the rotating stirrer (71) forming the freesurface (75), over the top of the weir (74), and then verticallydownward past the rotating stirrer (72), then exiting the stirringdevice (34) into the finer (73).

In the prior art, the downcomer pipe (7) is the primary resistance toglass flow through the delivery system (10) to the overflow process.Temperature control of the glass in the downcomer controls the glassflow. There is heating means, primarily electric, in the downcomer pipe(7), which controls the glass viscosity distribution in the downcomerpipe (7). There is a glass free surface in the bowl (6), whichdetermines the static pressure distribution in the downcomer pipe (7).Improved methods for controlling glass flow are discussed in U.S. PatentPublication No. 2006/0016219, which is incorporated herein by reference.

In the embodiment of the delivery system (70) in FIG. 7A, the stirringdevice has a free surface (75), but there is no free surface in thefiner (73), the cooling and conditioning pipe (5), or the transitionpipe (66) downstream of the stirring device. A free surface is animportant element in the control of glass flow. The glass flow in thisembodiment (70) is much more a function of the temperature distributionin the finer (73), the cooling and conditioning pipe (5), and thetransition pipe (66) than in the prior art. This can cause sluggishresponse (low bandwidth) in the control of glass flow. To overcome thesluggish response, the static pressure in the delivery system iscontrolled by the pumping action of the stirring device (34).

Most stirrer designs have a pumping action. U.S. Pat. No. 6,763,684 isan example and is incorporated herein by reference. FIG. 7B is a sectionthrough the stirring device (34) in FIG. 7A showing two stirrers (71 and72). In this embodiment, the rotational speed of the stirrers (71 and72) is used to alter the hydrostatic pressure in the delivery system.The stirrers (71 and 72) may be either the same or different in designand rotate in either the same or opposite directions.

For the purpose of explanation, consider that there are two identicalstirrers (71 and 72), which rotate in the same direction. The stirrers(71 and 72) are designed to produce moderate pumping action(approximately 25 to 250 mm of glass, assume 100 mm of glass for thisexample) at the design rotational speed. The pumping action is measuredas a difference between the height of the glass free surface (75) when astirrer is rotating versus the height of the glass free surface (75)when a stirrer is not rotating. When the stirrers (71 and 72) arestationary, the hydrostatic pressure in the molten glass (16) at theinlet (78) of the stirring device (34) is slightly higher than thehydrostatic pressure in the molten glass (16) at the finer inlet (73)because of the pressure loss due to Newtonian fluid flow. The moltenglass (16) passes up through stirrer (71), which rotates to increasehydrostatic pressure, and the glass passes down through stirrer (72),which, rotating in the same direction as stirrer (71), decreaseshydrostatic pressure. When the stirrers are rotating, the hydrostaticpressures at the inlet (78) of the stirring device (34) and the finerinlet (73) are still substantially the same, but the free surface (75)of the glass in the stirring device chamber (34) is higher by 100 mm(the design pumping action) than when the stirrers are stationary. If itis determined that the glass flow has decreased, a rapid increase in theflow to the predetermined value may be obtained by increasing thehydrostatic pressure at the finer inlet (73). This is accomplished byincreasing the rotational speed of the stirrer (71) and decreasing therotational speed of the stirrer (72). A 5% change in rotational speed ofeach stirrer will produce a 10% change (10 mm of glass) in staticpressure at the finer inlet (73). The homogenization of the glass willremain approximately the same as there will be approximately a 5%increase in mixing by the stirrer (71) and approximately a 5% decreasein mixing by the stirrer (72).

The pumping stirrer speed change strategy for controlling glass flowrate is directly applicable to the prior art configuration shown in FIG.1 with no other components of this invention. In an implementation ofthe delivery system which has a free surface in the bowl, changing therelative speeds of the stirrers as described above would increase thelevel of the free surface in the bowl, thus increasing the hydrostatichead for flow in the downcomer pipe. The stirring device control actionas applied to either an embodiment of this invention or to the prior artincreases the flow control bandwidth. It would be used to correct flowerrors until stable thermal control is restored, at which time thestirrer rotational speeds would return to normal.

In many industrial processes an auger type device is used to mix or pumpliquid or slurry material. The stirring device in the delivery system ofthe present invention preferably includes one or more augers, orstirrers. At the outflow tip of the stirring device is a region ofvortex flow, which does not readily mix with the main process stream.The material partially trapped in this region typically has differentmaterial and/or physical characteristics than the main process streamand is not homogeneous with the material in the process stream. Whenthis material mixes with the process stream, the defect in the productcaused by this inhomogeneous material that flows from the tip of anauger, or stirrer, is known as auger spot.

Referring to FIG. 7B, the formed section (77) is designed such that theinhomogeneous glass (76), which flows from the tip (79) of the stirrer(72), flows through an area (56) in the finer (50) as shown in FIG. 5and thus flows to an area (46) at the distal end of the formed sheet asshown in FIG. 4C. Therefore, the glass from the tip (79) of the stirrer(72) does not cause a defect in the salable portion of the glass sheet.This embodiment may be used with a stirring device (34) located ateither the inlet end of the finer (33), (73) in an embodiment of theinvention or the distal end of the finer (3) in the prior art.Relocating the stirring device (34) to the inlet end is preferred.

FIG. 7C is a section through the center of the stirrer (72) showing theshape of the formed section (77) relative to the tip (79) of the stirrer(72).

The glass that flows in proximity to the walls of the delivery system issubject to the development of inhomogeneities; including compositiongradients (cord), seeds, and, in the case of tin fined glass, platinumparticles. The tin in the glass, which is used as a fining agent,reduces platinum, thus producing platinum particles. Platinum has ahigher density than the glass, which normally would cause the particlesto drift to the bottom of the delivery system due to gravitationalforces; however, any platinum particles which have a high surface areato volume ratio will continue to flow in proximity to the deliverysystem walls. Referring back to FIG. 4B, those particles that flow inproximity to the wall in the areas (41) and (43) will end up in theformed sheet in the corresponding areas as shown in FIG. 4C.

U.S. Pat. No. 6,889,526 discusses ways to divert the flow in area (43)in FIG. 4B to the unusable end section (45) shown in FIG. 4C and isincorporated herein by reference. U.S. Pat. No. 6,895,782 discusses waysto divert the flow in areas (41 and 43) in FIG. 4B to the unusable endssections (45 and 47) shown in FIG. 4C and is also incorporated herein byreference.

FIGS. 8A through 8C show another embodiment of the present invention,which may be incorporated in any or all of the delivery systemembodiments (10, 30, 60 and 70). This embodiment includes a set of flowbaffles (81 and 83) at the exit end of the downcomer pipe (7). The topsurface of these baffles (81 and 83) is angled to the internal surfaceof the downcomer pipe (7) at an angle (82). Angle (82) varies from −10to 45 degrees. A comparison of FIGS. 4B and 8B shows that the flowbaffles (81 and 83) as shown in FIG. 8B are located at the same angularlocation in the downcomer pipe (7) as glass flows (41 and 43) and thusdivert the glass flow in these regions into the regions (44 and 46) ofthe downcomer pipe (7) as shown in FIG. 4B. These flow baffles (81 and83) are another technique for diverting the glass flow from the areas(41 and 43) in FIG. 4B to the unusable ends sections (45 and 47) shownin FIG. 4C. This embodiment may be used with the stirring device locatedat either the inlet end of the finer in an embodiment of this inventionor the distal end of the finer as in the prior art.

FIGS. 9A through 9D show various embodiments of the dual apex finercross-section in a shape termed “Gull Wing” herein. The embodiment inFIG. 9A is the same cross-section as shown in FIG. 5, but not at thefiner vent. The end corners have generous full radii (91) between thestraight sections. The embodiment in FIG. 9B has the same overall shape,but the corners (93) are shaped with no radii or chamfers between thestraight sections. The embodiment in FIG. 9C has chamfered corners (94)in between the straight sections. The embodiments in FIGS. 9A, 9B, and9C are shown to have no free surface in the cross-section. Theembodiment in FIG. 9D has smaller radii (95) at the ends and freesurface sections (99) at the apexes (57). The free surface section (99)is an extension of the vent back toward the stirring device a distance(112), as shown in FIGS. 11A and 11B. This provides for a larger area ofthe glass free surface (98). The free surface (98) length (112) may bethe entire length of the finer if desired. It may even extend into thecooling and conditioning section (5). Referring to FIG. 9B, the ratio ofthe overall width (97) of the finer to the width (96) between the apexes(57) of the finer is between 1.15 and 2.25. In a preferred embodiment,this width ratio is between 1.25 and 1.75.

FIGS. 10A, 10B, 10C, and 10D show additional embodiments of the dualapex finer cross-section. The embodiment in FIG. 10A is the same as FIG.9A but with a flat bottom (101). The embodiment in FIG. 10B has bottomsections (102), which form a V shape and generous end radii (106). Anadvantage of this embodiment is that any heavy particles in the glasswill migrate to the section (56), which will form the unusable distaledge of the sheet. This would be useful if large platinum particles arethe result of tin, in a tin refined glass, reducing the platinum wallsof the delivery system. The embodiment in FIG. 10C is a dual apexmodification to a cylindrical prior art finer. The bottom is circular(103) and the apexes are formed by smaller radii. This embodiment wouldhave a large part of the structural integrity of the cylindrical shapedfiner, but would not have the refining efficiency of a flat finer. Theembodiment in FIG. 10D is an elliptical shaped dual apex finer. Thebottom (104) is a large ellipse and the two apexes (57) are formed bytwo smaller ellipses (105) radiused together. This finer would have ahigher fining efficiency than the dual apex cylindrical finer in FIG.10C.

The ratio of finer cross-sectional area to finer height is indicative ofthe relative fining performance of a finer design. The larger the areafor flow, the slower the molten glass moves through the finer, allowingmore time for the seeds to rise. The lower the height of the finer, theless distance the seeds must rise. The ratio of the two parameterscreates an additional parameter termed “performance ratio” herein. Thehigher the performance ratio, the more efficiently the finer removes theseeds. The performance ratio is a figure of merit, not an exactdetermination of performance, especially when the finer cross-sectionalshapes become more complex.

FIGS. 20 through 29 show various finer cross-sections taught in U.S.Pat. No. 7,150,165 and U.S. Patent Publication 2007/0084247. The shapesof the cross-sections in FIG. 27A through 27H all have the sameperimeter, therefore the cost of construction is substantially equal.Table 1 shows the height, width, cross-sectional area, width to heightratio (aspect ratio) and performance ratio for each cross-sectionalshape.

TABLE 1 Aspect Performance FIG. Height Width Ratio Area Ratio 27A 0.31830.3183 1.00 0.0796 1.00 27B 0.1497 0.4489 3.00 0.0528 1.41 27C 0.25000.2500 1.00 0.0625 1.00 27D 0.1250 0.3750 3.00 0.0469 1.50 27E 0.13670.4102 3.00 0.0529 1.55 27F 0.1400 0.4200 3.00 0.0546 1.56 27G 0.13960.4188 3.00 0.0545 1.56 27H 0.1383 0.4148 3.00 0.0547 1.58

The perimeter of all of the shapes is the same, normalized to 1.00 unitof distance, thus the comparisons in Table 1 are between shapes with thesame cost of raw materials. In order to simplify the comparisons betweenthe performance ratios (cross-sectional area divided by height) of thevarious shapes, the performance ratio of the prior art cylindrical finer(FIG. 27A) has been adjusted to 1.00. This was done by multiplying thearea divided by the height by a factor of four.

FIG. 27A shows the cylindrical cross-section as known in the prior art.The cylindrical finer has an aspect ratio of 1.00 and a performanceratio of 1.00. In contrast, the cross-sectional shape of the finer ofthe present invention preferably has a width to height ratio (aspectratio) substantially greater than 1.00. The aspect ratio of the finer ispreferably 1.50 or greater. In a preferred embodiment, the aspect ratioof the finer is approximately 3.00. In another preferred embodiment, theaspect ratio of the finer is approximately 6.00.

FIG. 27B shows an elliptical cross-section of a finer of the presentinvention, with an aspect ratio of 3.00. Its performance ratio is 1.41,which means that it removes seeds more quickly than the cylindricalcross-section of FIG. 27A.

FIG. 27C shows a square cross-section of a finer. Since its performanceratio is 1.00, it removes seeds with approximately the same efficiencyas the finer with the cylindrical cross-section in FIG. 27A.

FIG. 27D shows a rectangular cross-section of a finer of the presentinvention. This finer has an aspect ratio of 3.00 and a performanceratio of 1.50. This finer removes seeds substantially quicker than thefiner with the cylindrical cross-section, shown in FIG. 27A, or thefiner with the square cross-section, shown in FIG. 27C.

FIGS. 27E, 27F, 27G and 27H are various embodiments of a finer with asubstantially rectangular cross-section. All of these embodiments havean aspect ratio of 3.00. The finer in FIG. 27E has a rectangularcross-section with sides, or corners, which are preferably chamfered orcurved. FIG. 27F shows a rectangular cross-section with rounded orcurved sides. FIG. 27G shows a rectangular cross-section with rounded orcurved sides and an arced top and bottom. This design increasesstructural rigidity. FIG. 27H is similar to the shape of FIG. 27G,except that its top (278) and bottom (279) surfaces are not parallel.The flow velocity at the center of the parallel top (278) and bottom(279) surfaces in FIG. 27G is slightly faster than at the sides (271).The cross-section in FIG. 27H has a bottom surface (279), which is arcedmore than the top surface (278), making the vertical distance (270) atthe center slightly less. This altered cross-section both slows therelative velocity of the glass at the center and decreases the distancethat seeds must rise. This equalizes the fining performance over agreater percentage of the width of the finer.

FIG. 28A through 28H and FIG. 29A through 29H show additional finershapes that provide increased fining capability. In FIG. 28A throughFIG. 28H, the top of the finer has a gabled roof shape that has an apexor ridge (283) with an obtuse included angle (280) to allow the seeds tomigrate to the center of the finer where they will more easily bedissipated at the atmospheric vent. In some embodiments of thisinvention, the migration of the seeds to the apex (283) of the finer isenhanced by narrow fining ribs (296) attached to the top surfaces (281)of the finer. These fining ribs (296) also provide structuralreinforcement of the finer top surface (281).

FIG. 28A shows a finer cross-section that is pentagonal with a slopedgabled roof (281), which has an obtuse angle (280) at its center (283).The sides (284) of the cross-section are parallel. As the obtuseincluded angle (280) approaches 180 degrees, the general shape issubstantially rectangular. The height at the center (288) is greaterthan the height at the ends (289). FIG. 28B shows a finer cross-sectionwith six sides where the tops (281) and opposite bottoms (282) areparallel and the ends (284) are parallel. A roof vent (298) of width(297) is also provided. FIG. 28C shows a finer cross-section with sixsides where the tops (281) and opposite bottoms (282) are parallel andthe ends (284) are perpendicular to the tops and bottoms. Fining ribs(296) with a center opening (295) are also shown. FIG. 28D shows thecross-section of FIG. 28B with single chamfers (285) at the ends (284).Fining ribs (296) with a center opening (295) are also shown. A roofvent (298) of width (297) is also provided. FIG. 28E has six sides andradiused (286) ends (284), where the top radii (286) and the bottomradii (286) are of different sizes. The tops (281) and the bottoms (282)of FIG. 28E are not parallel and the bottoms (282) are angled such thatthe height (288) at the center (283) is less than the height (289) atthe ends (284). FIG. 28F shows the cross-section of FIG. 28B withchamfered (285) top ends and radiused (286) bottom ends (284). A roofvent (298) is also provided. FIG. 28G shows the cross-section of FIG.28C with fully radiused (286) ends (284). FIG. 28G also has a horizontalbottom section (287) such that the height (288) at the center is greaterthan the height (289) at the ends (284). FIG. 28H shows thecross-section of FIG. 28D with chamfered (285) ends (284), where thechamfers are of different sizes. A roof vent (298) is also provided.

In FIGS. 29A through 29H, the top of the finer has a gothic arch shape(291), which has an apex (283) to allow the seeds to migrate to the apex(283) of the finer where they will more easily be dissipated at theatmospheric vent. In some of the preferred embodiments of thisinvention, the migration of the seeds to the apex (283) of the finer isenhanced by narrow ribs (296) attached to the top surfaces (291) of thefiner. These fining ribs (296) also provide structural reinforcement ofthe finer top surface (291).

The gothic arch shape (291) is a structural improvement over thestraight sided top surfaces (281) of FIGS. 28A through 28H. At the hightemperature of operation, a straight sided unsupported platinum roof(281) of the finer has the tendency to deform. In contrast, a gothicarch (291) has a natural structural stiffness that resists deformation.A finer, where there is no internal glass free surface, would primarilyhave a deformation problem during start-up conditions because, once thefiner is full of glass, the hydrostatic head of the glass in the finerprovides a force to make the platinum press against the refractorybacking material. The deformation of the top surface (281) and (291) ismost critical for a finer where the glass has an internal glass freesurface.

The top surfaces (291) in FIG. 29A have the shape of a gothic arch withan obtuse included angle (280) at the apex or ridge (283), an obtuseincluded angle (290) at the ends (284), a flat bottom (292), andparallel ends (284). FIG. 29B has top surfaces (291) the shape of agothic arch with the bottom surfaces (292) having a contour which isequidistant from the top surfaces (291), parallel ends (284) and an apexvent (also called a ridge vent (298)) of width (297) at the apex (283).FIG. 29C has top surfaces (291) the shape of a gothic arch with thebottom surfaces (292) having a contour which is equidistant from the topsurfaces (291) and ends (284) that form a right angle with the bottomsurfaces (292). FIG. 29C also has a horizontal bottom section (287) suchthat the height (288) at the center is greater than the height (289) atthe ends (284). Fining ribs (296) with a center opening (295) are alsoshown. FIG. 29D shows the cross-section of FIG. 29B with single chamfers(285) at the ends (284). Fining ribs (296) with a center opening (295)and an apex vent (298) are also shown. FIG. 29E has top surfaces (291)the shape of a gothic arch with a contoured bottom surface (292) whichhas a vertical distance (288) from the apex (283) which is less than theheight (289) at the ends (284) and has radiused ends (286) of differentradii. FIG. 29F shows the cross-section of FIG. 29B with chamfered (285)top ends and radiused (286) bottom ends (284). FIG. 29G shows thecross-section of FIG. 29C with fully radiused (286) ends (284). FIG. 29Hshows the cross-section of FIG. 29D with chamfered (285) ends (284)where the chamfers are of different sizes. In FIG. 29H, fining ribs(296) without a center opening and an apex vent (298) with width (297)are also shown.

FIGS. 28F, 28H, 29F, and 29H show a structural element (299) connectingthe top surfaces (281). This structural element maintains the apex ventat a constant width (297). In a preferred embodiment, the structuralelements (299) are webs with the web surfaces parallel to the directionof glass flow. The webs (299) are spaced at intervals along the apex(283) to provide the required structural strength. In another preferredembodiment the webs extend the distance between the fining ribs (296),but have openings at the fining ribs to allow the seeds to move from thefining rib (296) into the apex vent (298). In another preferredembodiment, the structural elements are struts spaced along the apex(283) at intervals to provide the required structural strength.

The fining ribs (296) shown in FIGS. 28C, 28D, 28H, 29C, 29D, and 29Htrap seeds moving in the direction of glass flow along the top surfaces(281) of the finer. The fining ribs (296) are a specific configurationof a baffle. The fining ribs are attached primarily to the top surfaces(281) of the finer and extend down from the top surface approximately 5to 40 percent of the height (288) of the finer. In addition to trappingseeds, they also provide structural reinforcement to the top surface ofthe finer. The seeds that are trapped agglomerate into larger seeds andthen migrate by buoyant force toward the ridge or apex (283). In FIGS.28C, 28D, 29C, and 29D, the fining rib is shown as ending at the edge(295) of the roof vent (298) where the seeds rise into the roof vent(298) and migrate in the direction of glass flow to the atmospheric ventat the outlet end of the finer. In FIGS. 28H and 29H, the fining rib(296) extends across the apex (283) of the finer and provides structuralstiffness in the manner of the structural element (289). The top of thefining rib (295) is open to the apex vent (298) such that the seeds riseinto the roof vent (298) and migrate in the direction of glass flow tothe atmospheric vent at the outlet end of the finer.

The apex vents (298) shown in FIGS. 28B, 28F, 29B, and 29F have aradiused cross-section, whereas the apex vents (298) shown in FIGS. 28D,28H, 29D, and 29H have a rectangular cross-section. The cross-sectionmay alternatively be triangular, trapezoidal, or pentagonal, etc. withradiused or chamfered corners. The apex vent (298) works in combinationwith the fining ribs (296) to allow the easy migration of seeds, whichhave moved to the apex (283) area through the action of the fining ribs(298), to the vent at the exit end of the finer.

FIG. 20A, 20B, and 20C show the range of the sizes of radii that willmaximize the fining efficiency for an enclosed finer. In FIG. 20A, theheight of the finer at its center is (203) and the total width is (201).A finer is considered an enclosed finer if the width (207) of the freesurface (208) of glass is less than 75 percent of the width of the finer(201). A rectangular finer where the top is horizontal and the glasscontacts the top over its entire width is considered an enclosed fineras shown in FIGS. 20B and 20C. FIG. 20A has the radius (204) of thebottom edge to side intersection equal to 20 percent of the height ofglass (202) in the finer and the radius (205) of the top edge to sideintersection equal to 20 percent of the height of glass (202) in thefiner. FIG. 20B has the radius (204) of the bottom edge to sideintersection equal to 50 percent of the height of glass (202) in thefiner and the radius (205) of the top edge to side intersection equal to50 percent of the height of glass (202) in the finer. In FIG. 20B, theradii are equal and comprise the extent of the edge of the finer. InFIG. 20C, the radius (205) of the top edge to side intersection is equalto 20 percent of the height of glass (202) in the finer and the radius(204) of the bottom edge to side intersection is equal to 50 percent ofthe height of glass (202) in the finer. Any combination of top andbottom radii within the 20 percent to 50 percent range would increasethe efficiency of the finer relative to the quantity of platinum used.

FIGS. 21A, 21B, and 21C show the range of the sizes of chamfers thatmaximize the fining efficiency for an enclosed finer. A finer isconsidered an enclosed finer if the width (217) of the free surface(218) of glass is less than 75 percent of the width of the finer (219).A rectangular finer whereby the top is horizontal and the glass contactsthe top over its entire width is considered an enclosed finer. In FIG.21A, the chamfer (214) of the bottom edge to side intersection is equalto 45 degree (°) by 14 percent of the height of the glass (202) in thefiner, and the chamfer (215) of the top edge to side intersection isequal to 45° by 14 percent of the height of the glass (202) in thefiner. In FIG. 21B, the chamfer (214) of the bottom edge to sideintersection is equal to 45° by 30 percent of the height of the glass(202) in the finer, and the chamfer (215) of the top edge to sideintersection is equal to 45° by 30 percent of the height of the glass(202) in the finer. The chamfers are equal in FIG. 21B. In FIG. 21C, thechamfer (215) of the top edge to side intersection is equal to 45° by 14percent of the height of the glass (202) in the finer, and the chamfer(214) of the bottom edge to side intersection is equal to 60° by 30percent of the height of the glass (202) in the finer. Any combinationof top and bottom chamfers between 45° and 60° by 14 percent to 30percent of the height of glass (202) in the finer increases theefficiency of the finer relative to the quantity of platinum used.

FIGS. 22A, 22B, and 22C show the range of the sizes of radii thatmaximizes the fining efficiency for a free surface finer. A finer isconsidered a free surface finer if the width (227) of the free surface(228) of glass is greater than 75 percent of the width of the finer(221). FIG. 22A shows a free surface finer with semi-circular sideswhere the top and bottom side radii (224) and (225) are equal to onehalf the height (223) of the finer cross-section. In FIG. 22B, theradius (224) of the bottom edge to side intersection is equal to 71percent of the height of the glass (222) in the finer, and the radius(225) of the top edge to side intersection is equal to 20 percent of theheight (223) of the finer. FIG. 22C has no radius at the top edge toside intersection of the finer. FIG. 22C has the radius (224) of thebottom edge to side intersection equal to 20 percent of the height ofthe glass (222) in the finer. Any combination of top radii within the 0and 50 percent of the height of the finer and bottom radii within the 20percent to 71 percent of the height of the glass in the finer increasesthe efficiency of the finer relative to the quantity of platinum used.

FIGS. 23A, 23B, and 23C show the range of the sizes of chamfers thatmaximize the fining efficiency for a free surface finer. A finer isconsidered a free surface finer if the width (227) of the free surface(228) of glass is greater than 75 percent of the width of the finer(221). In FIG. 23A, the chamfer (234) of the bottom edge to sideintersection is equal to 45° by 30 percent of the height (223) of thefiner and the chamfer (235) of the top edge to side intersection isequal to 45° by 30 percent of the height (223) of the finer. In FIG.23B, the chamfer (234) of the bottom edge to side intersection is equalto 45° by 71 percent of the height of the glass (222) in the finer andthe chamfer (235) of the top edge to side intersection is equal to 45°by 20 percent of the height (223) of the finer. FIG. 23C has no chamferat the top edge to side intersection of the finer. FIG. 23C has thechamfer (234) of the bottom edge to side intersection to be equal to 60°by 30 percent of the height (232) of the finer. Any combination of topchamfers within the 45° to 60° and 0 to 30 percent of the height of thefiner and bottom chamfers within the 45° to 60° by 30 percent to 71percent of the height of the glass in the finer increases the efficiencyof the finer relative to the quantity of platinum used.

FIGS. 24A through 24D illustrate embodiments of an inverted apex finerwhere the apex is pointed down (inverted) and the outside edges (244)are vertically the highest part of the finer cross-section. FIG. 25 is aview of a finer (251) with the cross-section similar to that in FIG.24A. The glass enters the finer (251) at the inlet end (253). In theseembodiments the seeds rise to the two outside edges and are dispersed toeither a vent, which spans the entire top of the exit end (254) of thefiner (251) or two separate vents (255) at the exit end (254) of thefiner (251). This configuration is especially adaptable to a singlecentral exit (254).

FIG. 24A shows the straight bottom elements (242) with an obtuse angle(240) at the inverted apex (243). The top elements (241) are parallel tothe bottom elements (242). The sides (244) are joined to the bottom andtop by equal radii (246). FIG. 24B shows the straight bottom elementsjoined at the inverted apex (243). The top elements (241) are parallelto the bottom elements (242). The sides (244) are joined to the bottomand top by unequal chamfers (245). A fining rib (247), which iscontinuous across the top surface, ends at each upper outside corner(249) to allow the seeds to flow toward the vents (255). FIG. 24C showscurved bottom elements (242) with an obtuse angle (240) at the invertedapex (243), which has the form of an inverted gothic arch. The topelements (241) are equidistant from the bottom elements (242). The sides(244) are joined to the bottom and top by unequal radii (246). FIG. 24Dshows curved bottom elements (242) joined at the inverted apex (243).The top elements (241) are equidistant from the bottom elements (242).The sides (244) are joined to the bottom elements (242) by an obtuseangle. The sides (244) are joined to the top elements (241) by cornervents (248), which conduct the seeds toward the exit end vents (255). Afining rib (247), which is continuous across the top surface, ends ateach upper outside corner (249) to allow the seeds to flow in the cornervents (248) toward the exit end vents (255). A preferred embodiment ofan inverted gabled roof finer has an obtuse included angle (240) of 140degrees. Obtuse included angles (240) between 190 degrees and 90 degreesare also within the spirit of the present invention. A preferredembodiment of an inverted gothic arch roof finer has an apex obtuseincluded angle (240) of 160 degrees and an end obtuse included angle(250) of 130 degrees. Additional obtuse included angles, in the range of178 degrees to 130 degrees for the apex obtuse included angle (240) and160 degrees to 90 degrees for the end obtuse included angle (250), arealso within the spirit of the present invention.

FIG. 26 shows an example of a finer (261) with an inlet (263), an outlet(264), and two atmospheric vents (265), which has multiplecross-sections. The finer (261) configuration has an inlet end (263)rectangular cross-section for a portion of the length of the finer(261), which transitions first to a rectangular cross-section withradiused ends (266), then to an inverted apex with radiused ends (262)and finally to a circular exit (264). The cross-sections in FIG. 26 alsohave different aspect ratios. The rectangular inlet (263) has an aspectratio of 2. The rectangular cross-section with radiused ends (261) andthe inverted apex with radiused ends cross-section (262) each have anaspect ratio of 3. The circular exit has an aspect ratio of 1. Thecombination of cross-sections and aspect ratios in FIG. 26 is just anexample of how the cross-sections and aspect ratios described herein maybe combined in a multiple cross-section finer.

In a preferred embodiment, the finer cross-section varies along itslength and incorporates by reference the cross-sections of U.S. Pat. No.7,150,165 and U.S. Patent Publication 2007/0084247, including thecross-sections shown in FIGS. 20 through 29, and also includes thecross-sections of FIG. 5, FIG. 9A through 9D, and FIGS. 10A through 10D.

FIGS. 11A and 11B show an embodiment (110) of the present inventionwhich has a large free surface (118) in the finer (113) and provisionsfor a glass free surface level measuring device (117). A free surfacesection (97) as shown in FIG. 9D extends a distance (112) back towardsthe stirring device (34) from the finer vent (115). The finer slopesdownward at an angle (119) such that the free surface (118) has aconstant depth. The angle (119) is designed to match the fluid head lossof the glass flowing in the finer (113). The free surface section (97)length (112) may be the entire length of the finer if desired. It mayeven extend into the cooling and conditioning section (5).

FIG. 11B shows an embodiment of the present invention whereby atraditional glass contacting level measuring device (117) is used. Theglass industry has used a glass contacting level measuring device for 50plus years. It is reasonably reliable and inexpensive, but often leavesa defect in the glass product when the glass it touches is part of thesaleable product. It can be used in the present invention because it isinstalled in one of the finer vents (115) where the glass it touchesends up in the unusable inlet edge (45) of the formed glass sheet asshown in FIG. 4C.

FIGS. 12A and 12B show an embodiment (120) of the present inventionwhich has a large free surface (118) in the finer (123) and provisionsfor a glass free surface level measuring device (127). The glassindustry has used a laser level measuring device for approximately 30years. It is reliable, but requires a line of sight that allowsreflection from the glass free surface (118). It is difficult toconfigure a laser level device in a traditional bowl (6) as shown inFIG. 1, but the long longitudinal distance (122) of the apex of a dualapex finer provides more than adequate room for installation. It can beused in the present invention because it is installed in one of thefiner vents (125), where the glass that is exposed to the atmosphereends up in the unusable inlet edge (45) of the formed glass sheet asshown in FIG. 4C.

FIG. 13 shows another embodiment (130) of the present invention wherebythe stirring device has pumping action that provides hydrostaticpressure for the glass to flow from the melting furnace (2) to theforming process. U.S. Pat. No. 6,763,684 discloses an example of astirrer with pumping action and is incorporated herein by reference. Thefiner (133) is angled up (139) such that the glass level of the glassfree surface (136) in the melting furnace is vertically below the bottom(138) of the cooling and conditioning pipe (135) by a distance (137),thus there is no glass flow by gravitational forces to the sheet formingapparatus when the stirrers are stationary. The stirrers in the stirringdevice (34) are engineered to produce enough hydrostatic pressure toovercome gravity and raise the glass level vertically above the bottom(138) of the cooling and conditioning pipe (135), thus providing glassflow to the sheet forming apparatus. This embodiment is an alternatemethod of stopping the flow to the sheet forming apparatus, to the priorart needle (13) shown in FIG. 1.

FIGS. 14A through 14D, FIGS. 15A and 15B and FIGS. 16A through 16D showembodiments of the present invention, which prevent platinum particlescaused by the reduction of platinum by tin from contaminating thesaleable portion of the glass sheet. Any platinum particles, which arecreated in the finer (153) or cooling and conditioning section (155),are confined to an area of the glass flow path that can be discarded bya glass overflow device at the downcomer pipe (7) to inlet pipe (158)interface (14).

FIGS. 14A through 14D show finer cross-sections, which have a freesurface (148) over the majority of the width of the finer. The advantageof this wide free surface (148) is that the tin in the glass does notcontact the platinum top surface of the finer and therefore does notchemically reduce the platinum. The embodiment in FIG. 14A has generousend radii (147), a flat top (149) and a shallow V shaped bottom (141).The embodiment in FIG. 14B has bottom sections (142) which form a Vshape and generous end radii (146). This would be useful if largeplatinum particles are the result of tin, in a tin refined glass,reducing the platinum walls of the delivery system. The embodiment inFIG. 14C is a cylindrical (143) finer modified to have a flat top (149).It has a free surface (148). This embodiment would have a large part ofthe structural integrity of the cylindrical shaped finer, but would nothave the refining efficiency of a high aspect ratio finer. Theembodiment in FIG. 14D is an elliptical shaped finer. The bottom (144)is a large ellipse and the top is formed by two smaller ellipses (145)connected together by the flat top (149). It has a free surface (148).This finer would have a higher fining efficiency than the cylindricalfiner in FIG. 14C. An advantage of the finer cross-sections with thewide top free surface (148) is that no platinum particles fall into thecenter of the glass stream. The particles with a low weight to volumeratio stay near the vertical and bottom surfaces. The particles with ahigh weight to volume ratio migrate down the vertical sides to thebottom surface. An advantage of the V shaped bottom and rounded bottomembodiments is that any high weight to volume ratio particles in theglass migrate to the section (56), which forms the unusable distal edgeof the sheet. The flat top (149) shown in the finers of FIGS. 14Athrough 14D is the most economical for platinum usage. An arched orcurved top may be preferable for structural reasons and could besubstituted for the flat top with no change in functionality.

FIG. 15A shows the principle parts of “The Overflow Process” glass sheetmanufacturing system (150) with a sloped finer with a full length freesurface and an overflow device at the downcomer to inlet pipe interfacein an embodiment of the present invention. The inlet pipe (158) has beenmodified to include an overflow device (151), from which flows a smallpercentage (154) of the total glass stream.

FIG. 15B shows a cross-section of a full length free surface finer(153), a cooling and conditioning section (155), and a transitionsection (156) shown in FIG. 15A containing a surface baffle (152) at thefiner vent (15) in an embodiment of the present invention. The finer(153) is sloped at an angle (159) equal to the hydrostatic pressure lossof the glass as it flows through the finer (153), thus the glass freesurface (158) slopes downward at the same angle (159). The free surfaceof the glass in the cooling and conditioning section (155) is curveddownward (157) as the hydrostatic pressure loss increases as the glassis cooled. A baffle (152) at the downstream side of the vent (15) trapsany surface bubbles such that they agglomerate, break-up, and vent tothe atmosphere.

FIG. 16A shows the location of the overflow device (151) at thedowncomer pipe (7) to inlet pipe (158) interface (14) in an embodimentof the present invention.

FIG. 16B is a view downward at section B-B in FIG. 16A. It shows the topof the inlet pipe (158) with the shape of the overflow device (151). Ina preferred embodiment, the centerline (167) of the downcomer pipe (7)is located a distance (161) from the centerline (162) of the inlet pipe(158) in a direction away from the overflow device (151). Thisfacilitates glass flow from the entire periphery of the downcomer pipe(7). The shape of the overflow device (151) shown is a typicalrepresentation. Its shape in a production implementation would bedetermined by mathematical and physical modeling, thus the overflowdevice (151) may have many configurations. Special heating andinsulation of the overflow device (151) is required and is known in theart. The quantity of glass (154) discarded in the overflow device (151)can vary from 1 to 20 percent of the total glass flow to the sheetforming apparatus. It would be 2 to 5 percent in a preferred embodimentof this invention.

FIG. 16C is a cross-section through the overflow device (151) showingthe bottom of the downcomer pipe (7) located a distance (165) below thefree surface (168) of the glass in the overflow device (151) in apreferred embodiment of this invention.

FIG. 16D is a cross-section through the overflow device (151) showingthe bottom of the downcomer pipe (7) located a distance (166) above thefree surface (168) of the glass in the overflow device (151) in apreferred embodiment of this invention.

The overflow device (151) can be designed for a specific location of thebottom of the downcomer pipe (7), which can be above, at, or below theglass free surface (168) in the overflow device (151). Additionally, theoverflow device (151) may be designed to discard the defective glass(154) over a range of the vertical locations of the bottom of thedowncomer pipe (7).

The overflow device (151) may be used as a stand alone embodiment tocorrect glass homogeneity problems at the downcomer pipe (7) to inletpipe (8) interface (14). U.S. Pat. Nos. 6,889,526, 6,895,782, 6,990,834,and 7,155,935, and U.S. Patent Publication Nos. 2007/0068197 and2007/0056323 address these problems and are incorporated herein byreference. Glass defects caused by vortex flow and quiescent flow at thedowncomer pipe (7) to inlet pipe (8) interface (14) can be eliminated bydiscarding the questionable glass (154) through the overflow device(151). The flow in this embodiment need not be continuous as discussedabove, but can be turned on periodically when defects in the glass sheetassociated with the downcomer pipe (7) to inlet pipe (8) interface (14)are found.

FIGS. 17A and 17B illustrate the application of the dual apex principleto a prior art delivery system (10) in an embodiment of this invention.FIG. 17A shows a stirring device (4) that feeds glass to a cooling andconditioning pipe (5) that in turn feeds glass to a modified bowl (176)that feeds glass to the downcomer pipe (7), which feeds glass to theforming process (8, 9, 11, and 16). FIG. 17B is view B-B in FIG. 17A,which shows the top of the bowl (176) that has been modified toincorporate two vents (175), which have free surfaces (178). Atraditional glass contacting level measuring device (177) has beeninstalled in one of the vents (175). The glass at the free surface (178)is subject to volatilization from exposure to the atmosphere, thusaffecting the glass homogeneity, and the measuring device (177) alsoaffects the quality of the glass surface. The vents (175) and themeasuring device (177) do not have an adverse effect on the productquality as the glass (174) that flows past the vents (175) of the bowl(176) flows in the areas (44) in the downcomer pipe (7) shown in FIG. 4Band thus forms the unsaleable inlet end portion (45) of the sheet asshown in FIG. 4C. The glass (173) that flows between the vents (175) isnot disturbed by the free surfaces (178) as it is in continuous contactwith the internal platinum surfaces of the delivery system. This glass(173) flows in areas (43) in the downcomer pipe (7) shown in FIG. 4B andthus forms a portion (43) of the surface of the sheet as shown in FIG.4C.

FIG. 18 shows another embodiment of a delivery system (180) of thepresent invention, where the bowl (6) in the prior art is replaced by abowl (186) with an overflow device (181). There is a glass free surface(188) in the overflow device (181), which is the same as the freesurface normally in the bowl (6). The glass (184) which flows out of theoverflow device (181) contains the glass which flows at the top surfaceof the finer insuring high quality glass flow to the overflow process.The finer vent (35) shown is optional as the glass defects which wouldnormally escape through the finer vent (35) are part of the glass flow(184) exiting through the overflow device (181). A needle (13) isoptionally provided to stop glass flow.

FIG. 19 shows another embodiment of a delivery system (190) of thepresent invention, where the bowl (6) in the prior art is replaced by abowl (196) with an overflow device (191). The finer bottom is angleddown (199) such that there is a glass free surface (198) in the finer(193), the cooling and conditioning section (195), and the overflowdevice (191). The glass (194) which flows out of the overflow device(191) contains the glass which flows at the top surface of the finer,insuring high quality glass flow to the overflow process. A needle (13)is optionally provided to stop glass flow.

The major components of the overflow downdraw manufacturing process arethe melting furnace, the delivery system, and the sheet formingapparatus. The length of the typical production campaign is presentlylimited by the life of the component which first fails or has degradedoperation. The prior art practice at this time is to rebuild all threecomponents when one component fails. This takes considerable time, notonly to dismantle and rebuild each component, but extensive cool downand reheat time is required for all components. The life of the meltingfurnace is limited by present technology to approximately two years. Thedelivery system, which is made primarily of precious metal, does nothave this inherent life limitation, but its practical life is four tosix years. The sheet forming apparatus has a life limitation ofapproximately two years unless the technology of U.S. Pat. No.6,889,526, U.S. Pat. No. 6,895,782, U.S. Pat. No. 6,990,834, U.S. Pat.No. 7,155,935, U.S. Patent Publication 2006/0016219, and U.S. PatentPublication 2007/0068197, all herein incorporated by reference, isimplemented, in which case a life of four years is likely achievable.

In FIG. 1, the fixed connection of the delivery system (3) to themelting furnace (2) at point (19) is a major impediment to repairingonly the melting furnace. Keeping the delivery system and the sheetforming apparatus at elevated temperature and fabricating this solidconnection is a problem. FIG. 30 is an embodiment of the presentinvention whereby this connection is not a fixed connection, but is afluid connection, thus the two components are easily disconnected andreconnected. Additionally, the interconnection is both adjustable andflexible. FIG. 30 shows a melting furnace (302) that has a forebay(309), which has a glass free surface (306) a vertical distance (307)below the bottom (308) of the finer (303). The stirring device (304),which has a significant pumping action, extends down into the freesurface of the glass (306) and pumps the glass into the finer (303),thus feeding molten glass (16) to the sheet forming apparatus.

FIGS. 31A and 31B show additional detail of two embodiments of aconnection between the melting furnace (302) and the stirring device(304). The stirring device has a stirrier (311), which may havedifferent configurations, two of which would be either an auger or oneof the mixing stirrer configurations of U.S. Pat. No. 6,763,684,incorporated herein by reference. FIG. 31A shows the bottom of thecasing (317) of the stirring device (304) extending below the glass freesurface (306) in the forebay (309) a distance (313). Stirrer (311)provides the hydrostatic pressure to raise the glass (16) to the finer(303) and subsequently to the sheet forming apparatus. A drawback ofthis configuration with some glasses would be the zones of quiescentflow (316) between the casing of the stirring device (304) and the wallsof the melting furnace (302) and the forebay (309). FIG. 31B shows aconfiguration whereby the bottom of the casing (318) of the stirringdevice (304) is above the glass free surface (306) in the forebay (309)a distance (314). The bottom (319) of the stirrer (311) extends downbelow the free surface (306) in order to suck the free surface (315) ofthe glass into the bottom (318) of the casing of the stirring device(304). This configuration would not have the zones of quiescent flow(316).

FIG. 31A shows the bottom (319) of the stirrer (311) located verticallyabove the bottom (317) of the casing of the stirring device (304), andFIG. 31B shows the bottom (319) of the stirrer (311) located verticallybelow the bottom (318) of the casing of the stirring device (304). Thevertical positioning of the bottom (319) of the stirrer (311) relativeto the bottom (317 or 318) of the casing of the stirring device (304) isan operational parameter which may be altered in order to minimize thegeneration of glass homogeneity defects. FIG. 31A also shows the bottom(317) of the casing of the stirring device (304) shaped (310) in orderto facilitate smooth flow of the glass (16) into the stirring device(304).

FIGS. 32A and 32B show two examples of a fluid connection between themelting furnace (2) and the finer (3). FIG. 32A shows a fluid connectionthat is an overflow device (321). Molten glass (16) flows out of themelting furnace (2) through the overflow device (321) into a receivingchamber (322), which is attached to the finer (3) at a connection (329).FIG. 32B shows a fluid connection which is an adaptation of thedowncomer pipe (7) to inlet pipe (8) connection (14). The glass flowsfrom the melting furnace (2) into a bowl like chamber (326), then downthe downcomer pipe (327) into the finer (323) through an inlet pipe(328).

FIG. 33 shows an example of a fluid connection between the meltingfurnace (2) and a vacuum finer (333). A vacuum device (335) induces alow absolute pressure (vacuum) on the free surface (336) in the vacuumfiner (333) and removes any gaseous inclusions (seeds) that rise to thefree surface (336) of the molten glass (16) in the vacuum finer (333).In this embodiment, the vacuum in the vacuum finer (333) is used to drawthe molten glass (16) from the free surface (306) in the forebay (339)of the melting furnace (2), vertically through the upflow conduit (334)into the vacuum finer (333). The molten glass (16) then flows from thevacuum finer (333) into a downflow conduit (337), then to a stirringdevice (4), a cooling and conditioning pipe (5), a bowl (6), and then tothe downcomer pipe (7) from which it enters the sheet forming apparatus.

The embodiments of the present invention shown in FIGS. 30, 31A, 31B,32A, 32B, and 33 eliminate the prior art problem of thermal expansionmismatch between the melting furnace (2) and the delivery system (10) atpoint (19).

The embodiments of the present invention shown in FIGS. 30, 31A, 31B,32A, 32B, and 33 facilitate rebuilding only the failed or degradedcomponent(s) of the overflow downdraw process. These embodimentseliminate the need for a complete rebuild of all components when onlyone component fails. The melting furnace (302) could be rebuilt in placewhile the delivery system and the sheet forming apparatus are maintainedat an elevated temperature. Additionally, these embodiments would permitfabrication and preheating of a melting furnace (302) at a remotelocation in the factory and the movement, for example by crane or rail,of the preheated melting furnace (302) into the manufacturing position,while keeping the delivery system and sheet forming apparatus atelevated temperature. With the implementation of remote fabrication andpreheating of a melting furnace (302), the turnaround in productionoperation would be measured in days, not weeks. There would also besignificant cost savings by rebuilding individual components only whenrequired by manufacturing performance.

A key element of this invention is the matching of the flowcharacteristics of the delivery system with the flow properties of theoverflow downdraw sheet glass manufacturing process. Extensive modelingof glass flow in the overflow downdraw process has generated theknowledge of where the glass from the flow in the delivery system,specifically the downcomer pipe, ends up in the formed sheet. Thisknowledge allows a radical rearrangement of the delivery systemcomponents in comparison to the prior art. The delivery system of thepresent invention may include one or more of the following embodiments:the stirring device installed prior to the finer, the finer designedsuch that substandard glass is diverted to the unusable end sections ofthe formed glass sheet, a glass level measuring device installed in thefiner vents without adversely affecting glass quality, the finer venteliminated when using the apparatus with certain glasses, the bowlreplaced by a transition section, the glass that flows in proximity tothe internal delivery system surfaces diverted to the unusable endsections of the formed glass sheet, an overflow device to discardinhomogeneous and defective glass located either in the bowl or at thedowncomer to inlet pipe interface, and/or using the stirring device toincrease the bandwidth of flow control. Preferred embodiments of thedelivery system include combinations of one or more of the embodimentsdiscussed herein. These embodiments may also be used in combination withan adjustable and flexible connection between the melting furnace andthe delivery system.

Accordingly, it is to be understood that the embodiments of theinvention herein described are merely illustrative of the application ofthe principles of the invention. Reference herein to details of theillustrated embodiments is not intended to limit the scope of theclaims, which themselves recite those features regarded as essential tothe invention.

1. A molten glass delivery system comprising: a) a stirring device thatreceives molten glass from a melting furnace; and b) a finer thatreceives molten glass from the stirring device; wherein the stirringdevice homogenizes the glass prior to the glass entering the finer. 2.The molten glass delivery system of claim 1, wherein the finer comprisesa shape that diverts unusable glass to at least one unusable end sectionof a glass sheet.
 3. The molten glass delivery system of claim 2,wherein the shape of the finer comprises a double apex shapedcross-section, wherein apexes of the finer contain glass that will forman unusable inlet end of the glass sheet.
 4. The molten glass deliverysystem of claim 2, wherein the stirring device comprises at least onestirrer, wherein the shape of the finer comprises a shapedcross-section, and wherein glass that flows from a tip of a bottom ofthe stirrer form an unusable distal end of the glass sheet.
 5. Themolten glass delivery system of claim 2, further comprising: c) acooling and conditioning section that receives glass from the finer; andd) a transition section that receives glass from the cooling andconditioning section.
 6. The molten glass delivery system of claim 5,wherein the finer does not include a vent.
 7. The molten glass deliverysystem of claim 2, wherein the glass is a tin fined glass, and platinumparticles in the glass are diverted to at least one unusable end sectionof the glass sheet.
 8. The molten glass delivery system of claim 2,wherein the finer comprises at least one finer vent and at least oneglass level measuring device located at the finer vent.
 9. The moltenglass delivery system of claim 2, further comprising: c) a cooling andconditioning section that receives glass from the finer; d) a bowl thatreceives glass from the cooling and conditioning section; e) a downcomerpipe that receives glass from the bowl; and f) at least one flow baffleat an exit end of the downcomer pipe, wherein a top surface of thebaffle is angled to an internal surface of the downcomer pipe at anangle between −10 and approximately 45 degrees.
 10. The molten glassdelivery system of claim 2, further comprising: c) a cooling andconditioning section that receives the glass from the finer; d) atransition section that receives the glass from the cooling andconditioning section; e) a downcomer pipe that receives glass from thetransition section; and f) at least one flow baffle at an exit end ofthe downcomer pipe, wherein a top surface of the baffle is angled to aninternal surface of the downcomer pipe at an angle between −10 andapproximately 45 degrees.
 11. The molten glass delivery system of claim2, wherein the finer has a free surface over substantially its entirelength.
 12. The molten glass delivery system of claim 11, furthercomprising: c) a cooling and conditioning section that has a freesurface over substantially its entire length that receives glass fromthe finer; d) a transition section that receives the glass from thecooling and conditioning section; e) a downcomer pipe that receivesglass from the transition section; and f) at least one flow baffle at anexit end of the downcomer pipe, wherein a top surface of the baffle isangled to an internal surface of the downcomer pipe at an angle between0 and approximately 45 degrees.
 13. The molten glass delivery system ofclaim 11, further comprising: c) a cooling and conditioning section thathas a free surface over substantially its entire length that receivesthe glass from the finer; d) a transition section that receives theglass from the cooling and conditioning section; e) a downcomer pipethat receives glass from the transition section; and f) an overflowdevice at a bottom of the downcomer pipe which discards inhomogeneousand defective glass.
 14. The molten glass delivery system of claim 1,wherein the glass delivery system is part of an overflow downdrawprocess.
 15. The molten glass delivery system of claim 1, wherein thestirring device comprises a first stirrer and a second stirrer, whereinthe first stirrer and the second stirrer have pumping action, andwherein the stirring device alters glass flow by changing a rotationalspeed of the first stirrer and the second stirrer.
 16. The molten glassdelivery system of claim 15, wherein the first stirrer and the secondstirrer pump in opposite directions, whereby a glass flow rate isaltered by decreasing a rotational speed of the first stirrer andincreasing a rotational speed of the second stirrer.
 17. The moltenglass delivery system of claim 1, wherein the stirring device comprisesat least one stirrer that has pumping action, wherein the stirringdevice provides hydrostatic pressure to move the glass from a meltingfurnace, through the glass delivery system to a glass forming process.18. A molten glass delivery system comprising: a) a downcomer pipe thatreceives molten glass; and b) at least one flow baffle at an exit end ofthe downcomer pipe, wherein a top surface of the baffle is angled to aninternal surface of the downcomer pipe at an angle that varies from −10to approximately 45 degrees.
 19. A stirring device for a molten glassdelivery system comprising a first stirrer and a second stirrer, whereinthe first stirrer and the second stirrer have pumping action, whereinthe stirring device alters glass flow by changing a rotational speed ofthe first stirrer and the second stirrer.
 20. The stirring device ofclaim 19, wherein the first stirrer and the second stirrer pump inopposite directions relative to the glass flow, whereby a glass flowrate is altered by decreasing a rotational speed of the first stirrerand increasing a rotational speed of the second stirrer.
 21. A moltenglass delivery system comprising a stirring device that comprises atleast one stirrer with pumping action, wherein the molten glass deliverysystem is elevated with respect to a melting furnace, wherein thestirring device provides hydrostatic pressure to move glass againstgravitational forces from the melting furnace through the elevated glassdelivery system to a glass forming process.
 22. The molten glassdelivery system of claim 21, wherein the stirrer is below a free surfacein a forebay of the melting furnace.
 23. The molten glass deliverysystem of claim 22, wherein a bottom of a casing of the stirring deviceis below the glass free surface in the forebay.
 24. The molten glassdelivery system of claim 22, wherein a bottom of a casing of thestirring device is above the glass free surface in the forebay.
 25. Amolten glass delivery system comprising: a) a downcomer pipe thatreceives molten glass; and b) at least one overflow device at a bottomend of the downcomer pipe, wherein the overflow device discardsinhomogeneous and defective glass.
 26. A molten glass delivery systemcomprising: a) a cooling and conditioning section; and b) a bowl thatreceives glass from the cooling and conditioning section, wherein thebowl includes an overflow device that discards inhomogeneous anddefective glass.
 27. A molten glass delivery system designed for anoverflow downdraw process and comprising a finer wherein a shape of thefiner diverts unusable glass to unusable ends of a glass sheet.
 28. Themolten glass delivery system of claim 27, wherein the shape of the finercomprises a double apex shaped cross-section, wherein at least one apexof the finer contains glass that forms an unusable inlet end of theglass sheet.
 29. The molten glass delivery system of claim 27, furthercomprising a stirring device comprising at least one stirrer, whereinthe shape of the finer comprises a shaped cross-section, wherein glassthat flows from a tip of a bottom of the stirrer forms an unusabledistal end of the glass sheet.
 30. A molten glass delivery systemdesigned for an overflow downdraw process, comprising: a) a finer; b) acooling and conditioning section that receives the glass from the finer;and c) a transition section that receives the glass from the cooling andconditioning section, wherein the transition section does not have afree surface.
 31. A molten glass stirring system comprising at least onerotating stirrer comprising a tip, wherein the tip of the stirrer at anend of a flow path through the stirring system discharges into a conduitwhich conducts any glass flow from the tip to an unuseable portion of aglass sheet.
 32. The molten glass stirring system of claim 31, whereinthe glass stirring system is designed for the overflow downdraw process,wherein glass that flows from the tip of a bottom of the stirrer formsan unusable distal end of the glass sheet.
 33. A molten glass levelmeasuring system comprising at least one glass measuring device, whereinglass exposed to the measuring device flows to an unusable portion of aglass sheet.
 34. The molten glass level measuring system of claim 33,further comprising a finer comprising at least one finer vent, whereinthe glass level measuring device is located at the finer vent.
 35. Themolten glass level measuring of claim 33, further comprising a bowl,wherein the glass level measuring device is located at the bowl.
 36. Amolten glass delivery system designed for the overflow downdraw processand comprising: a) a stirring device that receives molten glass from amelting furnace, wherein the stirring device homogenizes the glass; b) afiner which has no vent that receives molten glass from the stirringdevice; c) a cooling and conditioning section that receives glass fromthe finer; and d) a transition section that receives the glass from thecooling and conditioning section; wherein the finer comprises a shapethat diverts defective glass to unusable ends of a glass sheet.
 37. Themolten glass delivery system of claim 36, wherein the shape of the finercomprises a double apex shaped cross-section, wherein apexes of thefiner contain glass that will form an unusable inlet end of the glasssheet.
 38. A molten glass delivery system comprising: a) a stirringdevice that receives molten glass from a melting furnace and homogenizesthe glass; b) a finer that receives molten glass from the stirringdevice; c) a cooling and conditioning section that receives glass fromthe finer; d) a bowl that receives the glass from the cooling andconditioning section; e) a downcomer pipe that receives glass from thebowl; and f) at least one flow baffle at an exit end of the downcomerpipe, wherein a top surface of the baffle is angled to an internalsurface of the downcomer pipe at an angle between 0 and approximately 45degrees.
 39. A molten glass delivery system comprising: a) a stirringdevice that receives molten glass from a melting furnace, wherein thestirring device has pumping action and homogenizes the glass; b) a finerthat receives molten glass from the stirring device; c) a cooling andconditioning section that receives glass from the finer; and d) atransition section that receives the glass from the cooling andconditioning section; wherein a bottom of the cooling and conditioningsection is above a level of glass in the melting furnace such that thepumping action of the stirring device is used to move glass into anoverflow downdraw process.
 40. A molten glass system comprising: a) amelting furnace comprising a forebay; b) a stirring device that receivesglass from the forebay of the melting furnace, comprising at least onestirrer with pumping action, wherein the stirrer is below a free surfaceof the glass in the forebay; and c) a finer that is elevated withrespect to the melting furnace and the forebay; wherein the stirrerprovides hydrostatic pressure to move glass upward against gravitationalforces from the melting furnace through the finer to a glass formingprocess.
 41. The molten glass system of claim 40, wherein a bottom of acasing of the stirring device is below the free surface of the glass inthe forebay.
 42. The stirring device of claim 40, wherein the bottom ofcasing of the stirring device is above the free surface of the glass inthe forebay.
 43. A method of replacing a melting furnace in a glassdelivery system, comprising the steps of: a) removing a nonfunctioningmelting furnace from the glass delivery system without dismantling theother components of the glass delivery system; and b) placing afunctioning melting furnace into a manufacturing position of the glassdelivery system.
 44. The method of claim 43, wherein the functioningmelting furnace in step (b) is a rebuilt or repaired version of thenonfunctioning melting furnace.
 45. The method of claim 43, wherein thefunctioning melting furnace in step (b) is a newly fabricated meltingfurnace.
 46. The method of claim 43, wherein steps (a) and (b) areperformed while the other components of the glass delivery system remainat elevated temperature.
 47. A molten glass delivery system comprising:a) a melting furnace; and b) a stirring device that receives glass fromthe melting furnace; wherein a connection between the melting furnaceand the stirring device is fluid.
 48. The molten glass delivery systemof claim 47, wherein the melting furnace is easily detachable from thestirring device.
 49. A molten glass delivery system comprising: a) amelting furnace; and b) a finer that receives glass from the meltingfurnace; wherein a connection between the melting furnace and the fineris fluid.
 50. The molten glass delivery system of claim 49, wherein themelting furnace is easily detachable from the finer.